Factors affecting the yield of oxidants from the reaction of manoparticulate zero-valent iron and oxygen

The corrosion of zero-valent iron (Fe-(s)(0)) by oxygen (O-2) can lead to the oxidation of organic compounds. To gain insight into the reaction mechanism and to assess the nature of the oxidant, the oxidation of methanol, ethanol, 2-propanol, and benzoic acid by the reaction of nanoparticulate zero-valent iron (nZVI) or ferrous iron (Fe[II]) with O-2 in the absence of ligands was studied. At pH values below 5, Fe-(s)(0) nanoparticles were oxidized by O-2 within 30 min with a stoichiometry of approximately two Fe-(s)(0) oxidized per O-2 consumed. The yield of methanol and ethanol oxidation products increased from 1% at acidic pH to 6% at pH 7, relative to nZVI added, Product yields from 2-propanol and benzoic acid were highest under acidic conditions, with little oxidation observed at neutral pH. At pH values below 5, product formation was attributable to hydroxyl radical (OH center dot) production through the Fenton reaction,. involving hydrogen peroxide and Fe(II) produced during nZVI oxidation. At higher pH values, the oxidation of Fe(II), the initial product of nZVI oxidation, by oxygen is responsible for most of the oxidant production. Product yields at circumneutral pH values were consistent with a different oxidant, such as the ferryl ion (Fe[IV]).